1.定义
当一个对象的内在状态改变时允许改变其行为,这个对象看起来像是改变了其类。
2.类图
3.实例
State
package headfirst.state.gumballstate;
public interface State {
public void insertQuarter();
public void ejectQuarter();
public void turnCrank();
public void dispense();
}
HasQuarterState
package headfirst.state.gumballstate;
public class HasQuarterState implements State {
GumballMachine gumballMachine;
public HasQuarterState(GumballMachine gumballMachine) {
this.gumballMachine = gumballMachine;
}
public void insertQuarter() {
System.out.println("You can't insert another quarter");
}
public void ejectQuarter() {
System.out.println("Quarter returned");
gumballMachine.setState(gumballMachine.getNoQuarterState());
}
public void turnCrank() {
System.out.println("You turned...");
gumballMachine.setState(gumballMachine.getSoldState());
}
public void dispense() {
System.out.println("No gumball dispensed");
}
public String toString() {
return "waiting for turn of crank";
}
}
NoQuarterState
package headfirst.state.gumballstate;
public class NoQuarterState implements State {
GumballMachine gumballMachine;
public NoQuarterState(GumballMachine gumballMachine) {
this.gumballMachine = gumballMachine;
}
public void insertQuarter() {
System.out.println("You inserted a quarter");
gumballMachine.setState(gumballMachine.getHasQuarterState());
}
public void ejectQuarter() {
System.out.println("You haven't inserted a quarter");
}
public void turnCrank() {
System.out.println("You turned, but there's no quarter");
}
public void dispense() {
System.out.println("You need to pay first");
}
public String toString() {
return "waiting for quarter";
}
}
SoldOutState
package headfirst.state.gumballstate;
public class SoldOutState implements State {
GumballMachine gumballMachine;
public SoldOutState(GumballMachine gumballMachine) {
this.gumballMachine = gumballMachine;
}
public void insertQuarter() {
System.out.println("You can't insert a quarter, the machine is sold out");
}
public void ejectQuarter() {
System.out.println("You can't eject, you haven't inserted a quarter yet");
}
public void turnCrank() {
System.out.println("You turned, but there are no gumballs");
}
public void dispense() {
System.out.println("No gumball dispensed");
}
public String toString() {
return "sold out";
}
}
SoldState
package headfirst.state.gumballstate;
public class SoldState implements State {
GumballMachine gumballMachine;
public SoldState(GumballMachine gumballMachine) {
this.gumballMachine = gumballMachine;
}
public void insertQuarter() {
System.out.println("Please wait, we're already giving you a gumball");
}
public void ejectQuarter() {
System.out.println("Sorry, you already turned the crank");
}
public void turnCrank() {
System.out.println("Turning twice doesn't get you another gumball!");
}
public void dispense() {
gumballMachine.releaseBall();
if (gumballMachine.getCount() > 0) {
gumballMachine.setState(gumballMachine.getNoQuarterState());
} else {
System.out.println("Oops, out of gumballs!");
gumballMachine.setState(gumballMachine.getSoldOutState());
}
}
public String toString() {
return "dispensing a gumball";
}
}
GumballMachine
package headfirst.state.gumballstate;
public class GumballMachine {
State soldOutState;
State noQuarterState;
State hasQuarterState;
State soldState;
State state = soldOutState;
int count = 0;
public GumballMachine(int numberGumballs) {
soldOutState = new SoldOutState(this);
noQuarterState = new NoQuarterState(this);
hasQuarterState = new HasQuarterState(this);
soldState = new SoldState(this);
this.count = numberGumballs;
if (numberGumballs > 0) {
state = noQuarterState;
}
}
public void insertQuarter() {
state.insertQuarter();
}
public void ejectQuarter() {
state.ejectQuarter();
}
public void turnCrank() {
state.turnCrank();
state.dispense();
}
void setState(State state) {
this.state = state;
}
void releaseBall() {
System.out.println("A gumball comes rolling out the slot...");
if (count != 0) {
count = count - 1;
}
}
int getCount() {
return count;
}
void refill(int count) {
this.count = count;
state = noQuarterState;
}
public State getState() {
return state;
}
public State getSoldOutState() {
return soldOutState;
}
public State getNoQuarterState() {
return noQuarterState;
}
public State getHasQuarterState() {
return hasQuarterState;
}
public State getSoldState() {
return soldState;
}
public String toString() {
StringBuffer result = new StringBuffer();
result.append("\nMighty Gumball, Inc.");
result.append("\nJava-enabled Standing Gumball Model #2004");
result.append("\nInventory: " + count + " gumball");
if (count != 1) {
result.append("s");
}
result.append("\n");
result.append("Machine is " + state + "\n");
return result.toString();
}
}
GumballMachineTestDrive
package headfirst.state.gumballstate;
public class GumballMachineTestDrive {
public static void main(String[] args) {
GumballMachine gumballMachine = new GumballMachine(5);
System.out.println(gumballMachine);
gumballMachine.insertQuarter();
gumballMachine.turnCrank();
System.out.println(gumballMachine);
gumballMachine.insertQuarter();
gumballMachine.turnCrank();
gumballMachine.insertQuarter();
gumballMachine.turnCrank();
System.out.println(gumballMachine);
}
}
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